1. Field of the Invention
The present invention relates to a keyboard apparatus in which a hammer assembly is pivoted by key depression through a whippen and a jack.
2. Description of the Related Art
Conventionally, a keyboard apparatus having action units has been known. As disclosed in Japanese Laid-open Patent Publication No. 2003-263152, action units of a keyboard apparatus for upright piano can be configured that when any of keys is depressed, a corresponding whippen is pivoted and a jack is pivoted relative to the whippen to drive a butt, thereby pivoting a corresponding one of hammer assemblies each having a hammer shank and a hammer.
In an action unit for upright piano of this type, the hammer shanks of the hammer assemblies are vertically disposed to enable the hammers to strike respective ones of strings which are vertically stretched. When any of the keys is released from being depressed after striking the string, the corresponding hammer assembly returns to a non-key-depression position by its own weight, a repulsive force of the string, and an urging force of a butt spring.
However, the return capability of the hammer assembly by the own weight is weak since the hammer shank is vertically disposed, and the urging force of the butt spring cannot be made large to avoid a deteriorated key depression feeling. Thus, a delay can be caused in the return of the hammer assembly when the key is repeatedly depressed. This is one of factors that cause the upright piano to have an inferior capability of repeated key striking compared to the grand piano.
Despite that the action units for upright piano having hammer shanks disposed vertically are relative large in height size, no substantial efforts have been made to reduce the height size of the action units.